The present invention relates to a rack and pinion steering gear and, more particularly, to a rack and pinion steering gear having a low friction yoke assembly.
A known rack and pinion steering gear includes a pinion gear that is rotatably mounted in a housing and is connected with a steering wheel of a vehicle. A rack bar extends through the housing and has opposite end portions connected with steerable vehicle wheels. Gear teeth formed on the rack bar are disposed in meshing engagement with gear teeth on the pinion gear. A yoke assembly is disposed in the housing to support and guide movement of the rack bar relative to the housing. The support provided by the yoke assembly helps to ensure proper lash between the gear teeth of the rack bar and the gear teeth of the pinion gear. Rack and pinion steering gears having this general construction are disclosed in U.S. Pat. Nos. 3,623,379, 4,811,813, and 5,357,845.
During operation of this known rack and pinion steering gear, the yoke assembly may be subjected to both heat and high loads. The heat is produced due to friction between the rack bar and the yoke assembly as the rack bar moves relative to a support surface of the yoke assembly. A high load may occur, for example, when a vehicle hits a pothole in the road surface. The impact load of the vehicle tire with the pothole is transferred to the rack bar through the vehicle tie rods. The rack bar, in turn, transfers a portion of the load to the yoke assembly.
Both the heat and the high loads may cause a deflection in the yoke assembly. As a result, the yoke assembly may fail to properly support the rack bar and tooth wear on the rack bar and/or on the pinion gear may develop. Thus, a need exists for a low friction yoke assembly that provides sufficient support to the rack bar under high load conditions.
The present invention is directed to a rack and pinion steering gear. The rack and pinion steering gear comprises a housing. A pinion gear is rotatably mounted in the housing. A rack bar is movable relative to the pinion gear. The rack bar has teeth in meshing engagement with the pinion gear. The rack and pinion steering gear further comprises a yoke assembly in the housing for supporting and guiding movement of the rack bar relative to the pinion gear. The yoke assembly comprises a yoke and a plurality of balls. The yoke has a first surface and a plurality of slots which intersect the first surface. Each ball is located in a respective slot. Each ball projects from its respective slot and beyond the first surface of the yoke when load conditions on the yoke assembly are below a predetermined level. Each ball is movable in its respective slot relative to the first surface of the yoke as load conditions on the yoke assembly change.